Change 'Width' to 'Layout' to match the hard-coded list of translatable theme features in get_theme_feature_list().

Merges [26905] to the 3.8 branch.

props janrenn.
fixes #26777.

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git-svn-id: http://core.svn.wordpress.org/branches/3.8@26834 1a063a9b-81f0-0310-95a4-ce76da25c4cd